Tony Blair will meet the Iranian foreign minister, Kamal Kharrazi, early next month as part of the coalition-building for the looming war against Iraq.

In the Downing Street talks, the highest-ranking between Britain and Iran since the 1979 revolution soured relations, Tehran is expected to pursue its interest in influencing a post-Saddam settlement.

The visit will enrage Israel, still smarting from Mr Blair's hospitality for the Syrian president, Bashar al-Assad, at Downing Street last month.

The meeting is scheduled to take place as part of a flurry of diplomatic activity by Mr Blair over the next few weeks to rally support for action against Saddam Hussein.

The prime minister is helping to forge a British-Spanish-Italian coalition in support of the US as a counterweight to the more sceptical approach of Germany and France.

But the US also needs to swing behind it as many of Iraq's neighbours as possible: so far only only Kuwait has provided unqualified support.

Iran has until now had an ambivalent approach towards war, regarding both Iraq and the US as hostile states.

According to an informed Iranian source, Tehran has opted to back, albeit only discreetly, what it sees as the winning side. Iran hopes that Mr Blair will use his influence in Washington to ensure that after Iraq, the US does not turn on Iran.

Mr Blair's invitation to Mr Kharrazi is an important diplomatic opening that could help Iran shed its status as a pariah state. Last year President George Bush dubbed Iran part of the "axis of evil" that also includes Iraq and North Korea.

Britain, in contrast with the US, has pursued a policy of 'constructive engagement' with Iran since 1997. The foreign secretary, Jack Straw, has made three visits to Tehran.

Mr Kharrazi was initially planning to meet only Mr Straw during his British visit but Mr Blair has cleared 30 minutes in his own diary.

The Iranian source said that Iran had adopted an increasingly positive view of Mr Blair because of Britain's recent spat with Israel over the Assad visit and Israeli attempts to block a British-sponsored conference on Palestinian reform in London.

While Iran is unlikely to join formally an anti-Iraq coalition, it is in a position to help in a host of different ways. News of Mr Blair's Iranian meeting came as the prime minister stepped up the tempo of his campaign to shore up the European Union's fragile commitment to war, if necessary, by a series of phone calls and visits to European colleagues.

In addition to a 15-minute phone conversation with John Howard, the conservative prime minister of Australia, Mr Blair also spoke to both his Turkish and Greek counter parts (Greece holds the EU presidency) and was due to talk last night with President Chirac of France, the wiliest critic of the US-UK stance.

Tonight, his most controversial EU ally, Silvio Berlusconi of Italy, will pay a 90-minute call to No 10. Tomorrow, instead of flying straight to Washington, Mr Blair will first fly to Madrid to see Jose Maria Aznar, the prime minister of Spain, still regarded as "sound" on the issue, along with Italy.

Mr Blair will see Mr Chirac face-to-face at next Tuesday's bilateral summit in Le Touquet.

Mr Straw also stepped up the pressure on Baghdad by publishing 10 questions - drawn from the report of the chief UN weapons inspector, Hans Blix - which President Saddam must answer or face the "serious consequences" of forcible disarmament.

In a significant warning to rebel Labour MPs, he also claimed that the 32-vote revolt in the Commons in November in support of a Liberal Democrat motion making war conditional upon a formal UN resolution, meant that "we have overwhelming endorsement for the position we have taken".

Mr Straw, evidently Mr Blair's spokesman on the Blix report, held a press conference at which he said: "The world would be a much, much more dangerous place if, at this stage, we were to allow the world's most aggressive rogue state to continue with its practices of concealment and deceit and, above all, the development and holding of poisons, diseases and other weapons of mass destruction."

· Labour's ruling NEC yesterday restated its belief that military action should be used "only as a last resort within the framework of the UN and in accordance with international law and [we] support the prime minister's preference to see a second security council resolution". It did not vote on a motion condemning US-UK policy from Mark Seddon.